No one.
Miners will just get smarter.
They will mine altcoins and exchange them for bitcoins.
I am not sure there are miners that can mine bitcoins and certain altcoins as well. If there were, it would be fabulous!
This.
Peercoin was occasionally above the profitability of BTC, and the day the halving came, difficulty exploded. The profitability of PPC is still above BTC, but the difficulty is actually starting to go down. Note that almost everybody with old miners have begun to do this or leave altogether, which is why the hashrate's going down. Not everybody is completely shutting down, hashrate has simply moved elsewhere.
